A large amount of the natural water on the Earth is sea water or brackish water that is not suitable for human consumption due to the presence of salts and sediments. So-called fresh water may likewise be unsuitable for human consumption, for example containing deleterious compounds, bacteria or other microorganisms. Furthermore, groundwater can become polluted by the actions of man. In such instances it is known to treat the water by filtration and chemical treatment steps.
Filtration involves passing water through a filter medium that stops pollutants and passes pure water. The filter medium must be cleaned or replaced when its capacity is met. A highly effective mobile filtration apparatus used by the military is the reverse osmosis water purification unit or "ROWPU."
Reverse osmosis is a method that effects the separation of solutes from a solution by causing the solvent to float through a membrane at pressures higher than the normal osmotic pressure. This is possible because of the phenomenon of osmosis. Osmosis is a phenomenon manifested by the diffusion of a solvent (such as water) through a semi-permeable membrane from an area of greater osmotic pressure (i.e., greater concentration of dissolved substance) to an area of lower osmotic pressure (i.e., lesser concentration of dissolved substance). In reverse osmosis, the solvent diffuses through a membrane filter leaving dissolved substances, such as salts and other contaminants, behind.
Reverse osmosis purification equipment is readily sized for a particular application simply by providing the requisite area of membrane and a suitable pump. Therefore, reverse osmosis purification units are ideally suited for use at remote sites, and are conveniently transported on trucks or trailers.
These units are available in various capacities and typically are carried on trucks having such pumps and conduits as necessary to filter water from available sources. In this apparatus, water is forced through a membrane that passes pure water and concentrates pollutants in the water on the upstream side of the membrane. In addition, it is periodically necessary to flush or backwash the ROWPU filtration membranes to release collected contaminants from the membrane. As the concentration of the contaminants in the raw water increases to a given limit, the throughput through the ROWPU decreases for a given pump head pressure. Also, the membrane may become caked with contaminants on the high pressure side.
As a byproduct of filtration and/or backwashing, the water on the upstream side of the membrane, known as "brine," carries a higher concentration of contaminants than the source water. Depending on the time used and the extent of contaminants in the source water, the concentration of contaminants in the brine or backwash can be sufficient to render the water unfit for discharge into natural watercourses, which could become polluted. As a result, part of the water carrying capacity of a mobile military unit is devoted to transporting brine and backwash to municipal or similar fixed installations for water treatment.
Conventionally, during military operations, the backwash is captured in hard walled water tankers. Once one tanker is filled, the composition of its contents are determined via well known analytical methods. The contents of the tanker are then chemically treated. The tanker's contents are analyzed a second time. This process continues until the contents in the tanker are brought into compliance with EPA limits for sewer system disposal. Once in compliance, the contents are taken to a sanitation disposal site and discharged. The process of collecting and transporting brine and backwash, and treating and safely discharging it, requires the commitment of time and equipment. For example, it is conceivable that several tankers may need to be staged and available for collection and transport functions, each having at least one associated person on duty, in order to support the continuous operation of a ROWPU. What is needed is a multi-functional modular water filtration unit that can be adapted to treat different brine compositions, and which can be used in the field to render brine and backwash sufficiently pure to be discharged in the same area where the source water was collected, or at least to meet the minimum environmental protection standards for discharge into municipal sewage systems. By treating the brine and backwash in the field, the present invention eliminates the costs of batch hauling and discharge fees associated with conventional means of treatment, reduces the risks of spillage and substantially decreases the man hour and equipment requirements associated with conventional treatment means.
The multi-functional modular water filtration unit as described herein may be easily interfaced to optimize throughput capacity versus extent of filtration, using parallel and serial configurations of filtration elements interconnected by reconfigurable fittings. in a similar manner, the filtration media can be conveniently and effectively modified to facilitate operation in a variety of circumstances and for different specific pollutants. In a preferred arrangement, a modular brine/backwash filtration unit coupled to a ROWPU can be configured using the filtration elements to treat backwash from an ROWPU sourced by a natural watercourse or municipal supply; to treat sanitary waste water from showers, laundry facilities and the like; to treat water potentially containing nuclear or biological contaminants; to remove chemical contaminants such as fuels; and to pre-treat municipal source water supplies, for example to eliminate chlorine that tends to damage reverse osmosis membranes.